Two US journalists shot dead on live TV (Third Lead)

An unidentified gunman on Wednesday shot dead a reporter and a cameraman on live television when they were interviewing a businesswoman, stunning viewers across the US.

Alison Parker was doing the interview at about 6.45 a.m. at Bridgewater Plaza near Moneta, Virginia, when shots rang out. Both women screamed, CNN reported.

As the camera fell to the ground, the audience caught the briefest glimpse of a man who appeared to be pointing a gun towards the downed cameraman.

The station immediately cut away to a shocked anchor in the studio of WDBJ channel. Reporter Parker, 24, and cameraman Adam Ward, 27, were killed.

The Bureau of Alcohol, Tobacco, Firearms and Explosives as well as the FBI launched a massive manhunt to track down Vester Flanagan, the alleged killer, who the law enforcement officials confronted on a highway where he shot himself, officials told CNN. However, it was not clear whether he was killed or injured.

The woman being interviewed, Vicki Gardner, executive director of the Smith Mountain Lake Regional Chamber of Commerce, was shot in the back and was in surgery.

The gunman was believed to have fired six or seven times, WDBJ general manager Jeff Marks said.

All schools in the area were shut down.

"We do not know the motive," Marks said.

He called the twin murders a "terrible crime against two fine journalists".

"Our hearts are broken," Marks said on air, explaining that Parker's and Ward's colleagues were "holding back tears".

Parker was the morning reporter for the Roanoke station and a native of Virginia. She started with WDBJ as an intern, her biography on the station's website said.

She previously worked with another CNN affiliate, WCTI, in Jacksonville, North Carolina.

She was a graduate of James Madison University's School of Media Arts and Design in Harrisonburg.